Desperately short of defenders (400+ Mad Hungarians at the gates of Iasi vs. about 200 brave Russian lads), I needed something using fewer troops than a U-formation (I had two militia and a spearman, plus my general). So I set my spears at a 45% angle just inside the gate, with my bodyguard a short distance opposite them.
The attackers coming through the gate turned toward the spearmen ... then took a full cavalry charge from the rear/left flank.
Result: Routing, confusion, dead enemy general, more routing and heroic victory.
It's high-risk to commit your general in the first charge, but it worked.